The purpose of this study is a determination of the chemical differences among the six hemoglobins found in normal rat red blood cells. This involves separation of the hemoglobins, separation of their chains and partial amino acid sequence analysis. The significance of these studies lies in relating such chemical differences to our findings that each of these six hemoglobins is synthesized to a maximum extent at different stages of maturation of the bone marrow erythroid cell. These studies offer the possibility of a clearer understanding of the mechanisms involved in multiple hemoglobin formation as well as erythroid cell maturation.